植物二酰甘油酰基转移酶基因(DGAT)研究进展

三酰甘油(TAG)是油料作物最主要的储藏脂类,二酰甘油酰基转移酶(DGAT,EC2.3.1.20)是TAG合成途径的限速酶,其主要作用是催化二酰甘油加上酰基脂肪酸形成三酰甘油.在植物中已发现了3种不同类型的DGAT基因,分别为DGAT1、DGAT2和DGAT3.该文对近年来国内外有关植物DGAT相关基因及其蛋白分类、定位、结构及其在脂肪酸合成、种子发育与萌发、幼苗发育、叶片新陈代谢等过程中的作用等研究进展进行综述.为提高油料作物种子油含量以及特定脂肪酸积累提供理论参考.     

DGAT相关基因研究进展

DGAT是一种甘油酰基转移酶（Diacylgycerol Acyltransferase,DGAT）,该酶与脂肪代谢、脂类在组织中的沉积有很大关系,它的主要作用机制是使二酰甘油加上脂肪酸酰基形成三酰甘油。编码该酶的基因有DGAT1和GAAT2,前者属于ACAT基因家族,后者属于MGAT1基因家族。本文综述了动物DGAT相关基因定位、结构、生物学效应及其多态性与生产性能的关系。     

二脂酰甘油酰基转移酶2 (DGAT2)基因研究进展

二脂酰甘油酰基转移酶2 (Acyl CoA: Diacylgycerol Acyltransferase 2, DGAT2)是生物体内的一种非常重要的酶, 其主要机制是使二酰甘油加上脂肪酸酰基辅酶A以共价健结合形成三酰甘油。编码该酶的基因有DGAT2和DGAT1。文章综述了DGAT2基因的发现、定位、结构、生物学效应及其遗传多态性与生产性能的关系, 并对其应用前景进行了展望。     

二酰基甘油酰转移酶与肥胖研究新进展

甘油三酯(TG)是真核细胞中最重要的能量储存形式,尽管它是正常生理所必需,但过量堆积,就会导致肥胖.因此抑制TG的合成可能改善肥胖以及与之相关的症状.脂酰辅酶A:二酰基甘油酰转移酶(DGAT)是以甘油二酯和脂酰辅酶A为底物,催化甘油三酯合成途径的最后一步反应的关键酶.DGAT1基因敲除(Dgat1-/-)小鼠对肥胖有抵抗力,并且增加了对胰岛素和瘦素的敏感性,这种小鼠对饮食诱导的脂肪肝也有抵抗力.此外,DGAT1的缺乏影响脂肪源性因子的表达和分泌,从而调节能量和葡萄糖的代谢.这些研究提示DGAT1有望成为治疗肥胖和2-型糖尿病的新靶点.     

潜在的防治肥胖及糖尿病靶标——DGAT

二酰基甘油酰基转移酶(DGAT)是甘油三酯(TG)合成的关键酶,催化TG合成的最后一步。DGAT有两种亚型:DGAT1和DGAT2。DGAT1缺陷的小鼠对胰岛素和瘦素的敏感性增加且可以抵抗饮食诱导的肥胖;DGAT2功能下调可明显降低肥胖小鼠肝脏TG含量,改善脂肪肝的形成。DGAT抑制剂可改善动物模型的高脂血症和脂肪肝。因此,DGAT有可能成为防治肥胖、糖尿病等代谢性疾病的新的药物靶标。该文详细阐述了DGAT的生理功能研究及其抑制剂的研究进展。     

花生DGAT3的生物信息学分析

三酰甘油(TAG)是真核细胞最重要的能量储存形式,而酰基-Co A:二酰甘油酰基转移酶(DGAT)是生物体内三酰甘油合成过程中的关键酶。DGAT分为DGAT1、DGAT2和DGAT3三个家族,其中DGAT1和DGAT2均为膜结合蛋白,而DGAT3为细胞质游离蛋白。花生DGAT3是第一种被发现的DGAT3家族成员,该酶的分子量为41±1.0 k D。通过生物信息学研究花生DGAT3的特性,对于进一步研究花生三酰甘油的合成过程以及通过生物工程提高花生产油量都有重要意义。     

拟南芥TAG1 基因对脂类合成调控作用的研究进展

三酰甘油(TAG)是真核生物中能量贮存的最主要形式。植物中贮存的三酰甘油是食用油类和工业用油的主要来源。TAG1基因的表达产物甘油二酯酰基转移酶(DGAT)能够调控三酰甘油的合成。as11是TAG1基因突变获得的脂类代谢相关突变体。该文概述了拟南芥(Arabidopsis thaliana)突变体as11的生物学特征及TAG1基因对脂类合成调控的最新进展。     

拟南芥TAG1基因对脂类合成调控作用的研究进展

三酰甘油（TAG）是真核生物中能量贮存的最主要形式。植物中贮存的三酰甘油是食用油类和工业用油的主要来源。TAG1基因的表达产物甘油二酯酰基转移酶（DGAT）能够调控三酰甘油的合成。as11是TAG1基因突变获得的脂类代谢相关突变体。该文概述了拟南芥（Arabidopsis thaliana）突变体as11的生物学特征及TAG1基因对脂类合成调控的最新进展。     

小鼠不同泌乳期乳腺脂肪合成相关基因的mRNA表达

为了研究小鼠不同泌乳期乳脂肪合成相关基因的表达规律, 文章采用荧光定量PCR检测了小鼠乳腺中与脂肪合成和分泌相关20个基因的mRNA相对表达丰度和表达差异。结果表明, 在乳腺中脂蛋白脂酶(LPL)、乙酰辅酶A羧化酶(ACACA)、硬脂酰辅酶A去饱和酶(SCD)、黄嘌呤脱氢酶(XDH)、嗜乳脂蛋白(BTN)、脂肪酸分化蛋白(ADFP)基因都具有高mRNA表达丰度 (表达丰度>5%), 脂肪酸转运体(CD36)、脂肪酸合成酶(FASN)、1-酰基甘油磷酸酰基转移酶(AGPAT6)和甘油酰基转移酶(DGAT)基因具有中等mRNA表达丰度(5%>表达丰度>1%), 与妊娠期乳腺基因的mRNA表达相比, 在泌乳期这些基因的mRNA表达均有显著上调(P<0.05), 并且ACACA、SCD、FASN、AGPAT6和DGAT等脂肪合成酶基因的表达在泌乳中期(12 d)最高, 而在泌乳初期(6 d)和泌乳末期(18 d)较低, 呈现低-高-低的表达模式。转录因子固醇调节元件结合蛋白(SREBF)基因在泌乳开始时mRNA表达增加, 在泌乳中期(12 d)表达有10倍上调, 其变化规律与脂肪合成酶基因的表达模式相同, 说明SREBF基因在小鼠乳腺脂肪合成酶基因的表达调控中发挥重要调节作用。     

小鼠不同泌乳期乳腺脂肪合成相关基因的mRNA表达

为了研究小鼠不同泌乳期乳脂肪合成相关基因的表达规律,文章采用荧光定量PCR检测了小鼠乳腺中与脂肪合成和分泌相关20个基因的mRNA相对表达丰度和表达差异。结果表明,在乳腺中脂蛋白脂酶(LPL)、乙酰辅酶A羧化酶(ACACA)、硬脂酰辅酶A去饱和酶(SCD)、黄嘌呤脱氢酶(XDH)、嗜乳脂蛋白(BTN)、脂肪酸分化蛋白(ADFP)基因都具有高mRNA表达丰度(表达丰度>5%),脂肪酸转运体(CD36)、脂肪酸合成酶(FASN)、1-酰基甘油磷酸酰基转移酶(AGPAT6)和甘油酰基转移酶(DGAT)基因具有中等mRNA表达丰度(5%>表达丰度>1%),与妊娠期乳腺基因的mRNA表达相比,在泌乳期这些基因的mRNA表达均有显著上调(P<0.05),并且ACACA、SCD、FASN、AGPAT6和DGAT等脂肪合成酶基因的表达在泌乳中期(12 d)最高,而在泌乳初期(6 d)和泌乳末期(18 d)较低,呈现低-高-低的表达模式。转录因子固醇调节元件结合蛋白(SREBF)基因在泌乳开始时mRNA表达增加,在泌乳中期(12 d)表达有10倍上调,其变化规律与脂肪合成酶基因的表达模式相同,说明SREBF基因在小鼠乳腺脂肪合成酶基因的表达调控中发挥重要调节作用。     

Intestinal acyl-CoA:diacylglycerol acyltransferase 2 overexpression enhances postprandial triglyceridemic response and exacerbates high fat diet-induced hepatic triacylglycerol storage

Intestinal acyl-CoA:diacylglycerol acyltransferase 2 (DGAT2) is important in the cellular and physiological responses to dietary fat. To determine the effect of increased intestinal DGAT2 on cellular and physiological responses to acute and chronic dietary fat challenges, we generated mice with intestine-specific overexpression of DGAT2 and compared them with intestine-specific overexpression of DGAT1 and wild-type (WT) mice. We found that when intestinal DGAT2 is present in excess, triacylglycerol (TG) secretion from enterocytes is enhanced compared to WT mice; however, TG storage within enterocytes is similar compared to WT mice. We found that when intestinal DGAT2 is present in excess, mRNA levels of genes involved in fatty acid oxidation were reduced. This result suggests that reduced fatty acid oxidation may contribute to increased TG secretion by overexpression of DGAT2 in intestine. Furthermore, this enhanced supply of TG for secretion in Dgat2^Int mice may be a significant contributing factor to the elevated fasting plasma TG and exacerbated hepatic TG storage in response to a chronic HFD. These results highlight that altering fatty acid and TG metabolism within enterocytes has the capacity to alter systemic delivery of dietary fat and may serve as an effective target for preventing and treating metabolic diseases such as hepatic steatosis.     

DGAT1 is not essential for intestinal triacylglycerol absorption or chylomicron synthesis

Dietary triacylglycerols are a major source of energy for animals. The absorption of dietary triacylglycerols involves their hydrolysis to free fatty acids and monoacylglycerols in the intestinal lumen, the uptake of these products into enterocytes, the resynthesis of triacylgylcerols, and the incorporation of newly synthesized triacylglycerols into nascent chylomicrons for secretion. In enterocytes, the final step in triacylglycerol synthesis is believed to be catalyzed primarily through the actions of acyl-CoA:diacylglycerol acyltransferase (DGAT) enzymes. In this study, we analyzed intestinal triacylglycerol absorption and chylomicron synthesis and secretion in DGAT1-deficient (Dgat1(-/-)) mice. Surprisingly, DGAT1 was not essential for quantitative dietary triacylglycerol absorption, even in mice fed a high fat diet, or for the synthesis of chylomicrons. However, Dgat1(-/-) mice had reduced postabsorptive chylomicronemia (1 h after a high fat challenge) and accumulated neutral-lipid droplets in the cytoplasm of enterocytes when chronically fed a high fat diet. These results suggest a reduced rate of triacylglycerol absorption in Dgat1(-/-) mice. Analysis of intestine from Dgat1(-/-) mice revealed activity for two other enzymes, DGAT2 and diacylglycerol transacylase, that catalyze triacylglycerol synthesis and apparently help to compensate for the absence of DGAT1. Our findings indicate that multiple mechanisms for triacylglycerol synthesis in the intestine facilitate triacylglycerol absorption.     

Thematic Review Series: Intestinal Lipid Metabolism: New Developments and Current Insights: Intestinal triacylglycerol synthesis in fat absorption and systemic energy metabolism

The intestine plays a prominent role in the biosynthesis of triacylglycerol (triglyceride; TAG). Digested dietary TAG is repackaged in the intestine to form the hydrophobic core of chylomicrons, which deliver metabolic fuels, essential fatty acids, and other lipid-soluble nutrients to the peripheral tissues. By controlling the flux of dietary fat into the circulation, intestinal TAG synthesis can greatly impact systemic metabolism. Genes encoding many of the enzymes involved in TAG synthesis have been identified. Among TAG synthesis enzymes, acyl-CoA:monoacylglycerol acyltransferase 2 and acyl-CoA:diacylglycerol acyltransferase (DGAT)1 are highly expressed in the intestine. Their physiological functions have been examined in the context of whole organisms using genetically engineered mice and, in the case of DGAT1, specific inhibitors. An emerging theme from recent findings is that limiting the rate of TAG synthesis in the intestine can modulate gut hormone secretion, lipid metabolism, and systemic energy balance. The underlying mechanisms and their implications for humans are yet to be explored. Pharmacological inhibition of TAG hydrolysis in the intestinal lumen has been employed to combat obesity and associated disorders with modest efficacy and unwanted side effects. The therapeutic potential of inhibiting specific enzymes involved in intestinal TAG synthesis warrants further investigation.     

Properties of phosphatidate phosphohydrolase and diacylglycerol acyltransferase activities in the isolated rat heart. Effect of glucagon, ischaemia and diabetes.

Myocardial triacylglycerol hydrolysis is subject to product inhibition. After hydrolysis of endogenous triacylglycerols, the main proportion of the liberated fatty acids is re-esterified to triacylglycerol, indicating the importance of fatty acid re-esterification in the regulation of myocardial triacylglycerol homoeostasis. Therefore, we characterized phosphatidate phosphohydrolase (PAP) and diacylglycerol acyltransferase (DGAT) activities, enzymes catalysing the final steps in the re-esterification of fatty acids to triacylglycerols in the isolated rat heart. The PAP activity was mainly recovered in the microsomal and soluble cell fractions, with an apparent Km of 0.14 mM for both the microsomal and the soluble enzyme. PAP was stimulated by Mg2+ and oleic acid. Oleic acid, like a high concentration of KCl, stimulated the translocation of PAP activity from the soluble to the particulate (microsomal) fraction. Myocardial DGAT had an apparent Km of 3.8 microM and was predominantly recovered in the particulate (microsomal) fraction. Both enzyme activities were significantly increased after acute streptozotocin-induced diabetes, PAP from 15.6 +/- 1.1 to 28.1 +/- 3.6 m-units/g wet wt. (P less than 0.01) and DGAT from 2.23 +/- 0.11 to 3.01 +/- 0.11 m-units/g wet wt. (P less than 0.01). In contrast with diabetes, low-flow ischaemia during 30 min did not affect PAP and DGAT activity in rat hearts. Perfusion with glucagon (0.1 microM) during 30 min did not affect total PAP activity, but changed the subcellular distribution. More PAP activity was recovered in the particulate fraction. DGAT activity was lowered by glucagon treatment from 0.37 +/- 0.03 to 0.23 +/- 0.02 m-unit/mg of microsomal protein (P less than 0.05). The role of PAP and DGAT activity and PAP distribution in the myocardial glucose/fatty acid cycle is discussed.     

Properties of the mouse intestinal acyl-CoA:monoacylglycerol acyltransferase,MGAT2

Acyl-CoA:monoacylglycerol acyltransferase (MGAT) plays an important role in dietary fat absorption by catalyzing a rate-limiting step in the re-synthesis of diacylglycerols in enterocytes. The present study reports further characterization of MGAT2, a newly identified intestinal MGAT (Cao, J., Lockwood, J., Burn, P., and Shi, Y. (2003) J. Biol. Chem. 278, 13860-13866) for its substrate specificity, requirement for lipid cofactors, optimum pH and Mg2+, and other intrinsic properties. MGAT2 enzyme expressed in COS-7 cells displayed a broad range of substrate specificity toward fatty acyl-CoA derivatives and monoacylglycerols, among which the highest activities were observed with oleoyl-CoA and rac-1-monolauroylglycerol, respectively. MGAT2 appeared to acylate monoacylglycerols containing unsaturated fatty acyls in preference to saturated ones. Lipid cofactors that play roles in signal transduction were shown to modulate MGAT2 activities. In contrast to oleic acid and sphingosine that exhibited inhibitory effects, phosphatidylcholine, phosphatidylserine, and phosphatidic acid stimulated MGAT2 activities. Using recombinant murine MGAT2 expressed in Escherichia coli, we demonstrated conclusively that MGAT2 also possessed an intrinsic acyl-CoA:diacylglycerol acyltransferase (DGAT) activity, which could provide an alternative pathway for triacylglycerol synthesis in the absence of DGAT. In contrast to the inhibitory effect on MGAT2 activities, nonionic and zwitterionic detergents led to a striking activation of DGAT activity of the human DGAT1 expressed in mammalian cells, which further distinguished the behaviors of the two enzymes. The elucidation of properties of MGAT2 will facilitate future development of compounds that inhibit dietary fat absorption as a means to treat obesity.     

Diacylglycerol acyltransferase 2 acts upstream of diacylglycerol acyltransferase 1 and utilizes nascent diglycerides and de novo synthesized fatty acids in HepG2 cells

The two diacylglycerol acyltransferases, DGAT1 and DGAT2, are known to have non-redundant functions, in spite of catalysing the same reaction and being present in the same cell types. The basis for this distinctiveness, which is reflected in the very different phenotypes of Dgat1(-/-) and Dgat2(-/-) mice, has not been resolved. Using selective inhibitors of human DGAT1 and DGAT2 on HepG2 cells and gene silencing, we show that, although DGAT2 activity accounts for a modest fraction (相似文献   

Effects of DGAT1 deficiency on energy and glucose metabolism are independent of adiponectin

Mice lacking acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), an enzyme that catalyzes the terminal step in triacylglycerol synthesis, have enhanced insulin sensitivity and are protected from obesity, a result of increased energy expenditure. In these mice, factors derived from white adipose tissue (WAT) contribute to the systemic changes in metabolism. One such factor, adiponectin, increases fatty acid oxidation and enhances insulin sensitivity. To test the hypothesis that adiponectin is required for the altered energy and glucose metabolism in DGAT1-deficient mice, we generated adiponectin-deficient mice and introduced adiponectin deficiency into DGAT1-deficient mice by genetic crosses. Although adiponectin-deficient mice fed a high-fat diet were heavier, exhibited worse glucose tolerance, and had more hepatic triacylglycerol accumulation than wild-type controls, mice lacking both DGAT1 and adiponectin, like DGAT1-deficient mice, were protected from diet-induced obesity, glucose intolerance, and hepatic steatosis. These findings indicate that adiponectin is required for normal energy, glucose, and lipid metabolism but that the metabolic changes induced by DGAT1-deficient WAT are independent of adiponectin and are likely due to other WAT-derived factors. Our findings also suggest that the pharmacological inhibition of DGAT1 may be useful for treating human obesity and insulin resistance associated with low circulating adiponectin levels.     

A molecular model for diacylglycerol acyltransferase from Mortierella ramanniana var. angulispora

Acyl CoA diacylglycerol acyltransferase (DGAT, EC 2.3.120) is recognized as a key player of cellular diacylglycerol metabolism. It catalyzes the terminal, yet the committed step in triacylglycerol synthesis using diacylglycerol and fatty acyl CoA as substrates. The protein sequence of diacylglycerol acyltransferse (DGAT) Type 2B in Moretierella ramanniana var. angulispora (Protein_ID = {"type":"entrez-protein","attrs":{"text":"AAK84180.1","term_id":"15099961"}}AAK84180.1) was retrieved from GenBank. However, a structure is not yet available for this sequence. The 3D structure of DGAT Type 2B was modeled using a template structure (PDB ID: 1K30) obtained from Protein databank (PDB) identified by searching with position specific iterative BLAST (PSI-BLAST). The template (PDB ID: 1K30) describes the structure of DGAT from Cucurbita moschata. Modeling was performed using Modeller 9v2 and protein model is hence generated. The DGAT type 2B protein model was subsequently docked with six inhibitors (sphingosine; trifluoroperazine; phosphatidic acid; lysophospatidylserine; KCl; 1, 2-diolein) using AutoDock (a molecular docking program). The binding of inhibitors to the protein model of DGAT type 2B is discussed.